The guest LAN's network is 192.168.2.0/24 and the firewall rules deny this network from reaching the main 192.168.1.0/24 network and the cable modem. Traffic from 192.168.1.0 is allowed to reach all hosts on 192.168.2.0, enabling easy management of servers on this network.
I have long since erased my default Linksys management firmware and replaced it with DD-WRT, so I can't demo how to do it with the software you probably already have. I will guess that there are no reasons why you can't set forwarding to the guest LAN on your router using the default management software. So, a simple DMZ setup would involve joining your server to the guest LAN with a static address, and telling your router to send requests to that host.
This should be a quick and simple solution for you since your guest LAN is already prohibited from connecting to your main network. I hope this home hosting howto works for you.